Efficient transmission of a command or data, sharing of information resources and sharing of hardware resources can be implemented by interconnecting a plurality of apparatus into a network. Further, attention is paid recently to a radio network as a system which releases a user from wiring according to a wired system.
As standard specifications relating to a radio network, the IEEE (The Institute of Electrical and Electronics Engineers) 802.11, HiperLan/2, IEEE 802.15.3, Bluetooth communication and so forth are available. In recent years, a radio LAN system has been popularized remarkably because it has become less expensive and is built as a standard element also in a PC.
A radio communication system of a comparatively small scale is used for data transmission between a host apparatus and a terminal apparatus in a home or the like. As an example of the host apparatus here, set down type domestic appliances such as a television set, a monitor, a printer, a PC, a VTR and a DVD player are available. Meanwhile, as an example of the terminal apparatus, mobile type apparatus whose power consumption is suppressed to the minimum such as a digital camera, a video camera, a portable telephone set, a personal digital assistant and a portable music reproduction apparatus are available. An application of a system of the type described is to upload image data taken up using a portable telephone set with a camera or a digital camera into a PC through a radio LAN or the like.
For example, a digital camera which is advantageous in that it performs Bluetooth communication favorably has been proposed (refer to, for example, Patent Document 1). A digital camera includes a case and a shutter button provided on the case, and the shutter button is provided at one of end portions in the leftward and rightward direction of an upper portion of the case. Further, an antenna for Bluetooth communication is provided at the other end portion in the leftward and rightward direction at an upper portion of the case within the case.
However, a radio LAN has been designed and developed originally supposing utilization with a computer, and where it is incorporated in a mobile type apparatus, the power consumption of the mobile type apparatus matters. Most of radio LAN cards of the IEEE 802.11b currently on the market exhibit power consumption of 800 W or more upon transmission and 600 W or more upon reception. The power consumption imposes a heavy burden on a battery-driven portable apparatus.
Even if a radio LAN function is caused to operate restrictively at a short distance to decrease the transmission power, the power consumption can be reduced only by approximately 80%. Particularly since transmission from an image inputting apparatus such as a digital camera to the image display apparatus side is performed in such a communication form that the transmission ratio occupies most of the entire communications, radio transmission measures of further reduced power consumption are demanded.
Further, in Bluetooth communication, the transmission rate is as low as 720 kbps at the highest, and it is inconvenient that much transmission time is required for transmission of an image which has been enhanced in the picture quality and increased in the file size recently.
In contrast, according to radio transmission which utilizes a reflected wave based on the back scatter system used in RFID, reduction in power consumption can be implemented, for example, in such a communication form that the transmission ratio between apparatus occupies most of communications.
A ratio communication system of the back scatter type includes a reflector for transmitting data in the form of a reflected wave for which a modulation process is performed, and a reflected wave reader for reading the data from the reflected wave from the reflector. Upon data transmission, the reflected wave reader transmits a non-modulated carrier. In contrast, the reflector applies a modulation process to the non-modulated carrier in accordance with transmission data using a load impedance operation such as, for example, turning on/off of termination of an antenna to signal the data. Then, the reflected wave reader side can receive the reflected wave and perform a demodulation and decoding process for the received reflected wave to acquire the transmission data.
The reflector includes an antenna for reflecting incoming a radio wave, for example, of a continuous wave, a generation circuit for transmission data, and an impedance variation circuit for varying the impedance of the antenna in accordance with the transmission data (refer to, for example, Patent Document 2).
In a reflected wave transmission system, an antenna switch for varying the load impedance of an antenna (that is, for performing modulation of a reflected wave) is usually formed from a gallium arsenide IC. The power consumption of the antenna switch is several tens μW or less, and the average power when data transmission is performed is 10 mW or less in the case of a delivery confirmation system and is several tens μW in one-way transmission with which data transmission can be performed. Where the average power is compared with average power consumption of a general radio LAN, it exhibits an overwhelming difference in performance (refer to, for example, the specification of Japanese Patent Application No. 2003-291809). Accordingly, even where a terminal apparatus for information storage is incorporated in a battery-driven mobile apparatus such as a digital camera, the battery life can be extended significantly by reducing the power consumption upon data transmission action.
FIG. 5 shows an example of a configuration of a radio data transmission system which utilizes a reflected wave transmission system.
The system shown includes a digital camera 101 with a reflected wave transmission function, a reflected wave reader 102, a television set 106, and an infrared remote controller 108. A video output of the reflected wave reader 102 is connected to an external video input terminal of the television set 106 by a video cable 105.
A non-modulated carrier 103 is transmitted from the reflected wave reader 102, and JPEG (Joint Photographic Experts Group) image data is returned as a reflected wave from the digital camera 101. The transmission of the image data is controlled from an operation section (hereinafter described) of the digital camera 101.
The infrared remote controller 108 provides a control signal to an infrared reception section 107 of the television set 106 and is used for changeover of a channel of the video or the like.
FIG. 6 schematically shows a configuration of a digital camera with a radio data transmission function. Reference numeral 200 denotes a digital camera with a radio data transmission function. The digital camera itself includes a camera section 202, a signal processing section 203, a memory card interface section 204, an operation/display section 205, a USB interface section 206, and a radio transmission module 208.
The signal processing section 203 converts image data inputted from the camera section 202 into image data of a predetermined format such as the JPEG format and stores the image data into an external memory card 207 through the memory card interface section 204.
The operation display section 205 performs image display, various settings and so forth. The USB interface section 206 is used to perform image transfer to a PC using the USB interface.
The radio transmission module 208 includes an antenna 209, an antenna switch 210, an antenna load 211, a band-pass filter 212, and an ASK detection section 213. In the present embodiment, the 2.4 GHz band is used as a frequency of radio waves.
Where image transfer is to be performed, when the radio transmission module 208 receives image data read out from the memory card 207 by the signal processing section 203, it performs on/off actions of the antenna switch 210 connected to the antenna 209 in accordance with a bit image of the data. For example, when the data is 1, the antenna switch 210 is turned on, but when the data is 0, the antenna switch 210 is turned off.
As seen in the figure, when the antenna switch 210 is on, the antenna 209 is terminated by the antenna load 211 of 50Ω, but when the antenna switch 210 is off, the antenna 209 is open. Since this action provides a behavior of termination of a radio wave arriving from a transfer destination when the antenna switch 210 is on and another behavior of reflection of the radio wave when the antenna switch 210 is off, the transfer destination can read image data by detecting reflection of a transmitted radio wave. In other words, image data is transmitted as a reflected wave of a radio wave from the transfer destination which is caused by variation of the antenna load impedance caused by on/off operations of the antenna switch 210, and so-called back scatter communication is implemented. A reflected wave signal from the radio transmission module 208 is equivalent to an ASK modulated wave. Further, also it is possible to produce a PSK modulated wave by varying the load impedance between an open state and a shorted state (antenna load 211=0Ω).
The antenna switch 210 is usually formed from a gallium arsenide IC and exhibits power consumption of several tens μW or less. According to the reflected wave transmission described above, the antenna switch 210 can implement radio image transmission of very low power transmission within a range of the transmission distance of up to approximately 5 m.
The band-pass filter 212 and the ASK detection section 213 are used upon reception of an ASK modulated delivery confirmation signal from the transfer destination. However, the two blocks are unnecessary for one-way transmission wherein delivery confirmation of transmission is not performed. On the other hand, where delivery confirmation is performed, the control therefor is performed by the signal processing section 203.
The band-pass filter 212 is used in order to pass a frequency of the 2.4 GHz band therethrough but attenuate the other frequency bands. The power consumption of the ASK detection section 213 necessary to perform delivery confirmation can be implemented with 30 mW or less.
Accordingly, the average power when the radio communication apparatus shown in FIG. 6 performs data transmission of image data or the like is 10 mW or less in the case of the delivery confirmation system but is several tens μW in the case of one-way transmission to achieve data transfer. This is an overwhelming performance difference when compared with the average power consumption of a general radio LAN.
FIG. 7 schematically shows a hardware configuration of the reflected wave reader which receives transmission data from the radio communication apparatus shown in FIG. 6.
As described hereinabove, image data is transmitted from the digital camera which it is carried on a reflected wave. Accordingly, the reflected wave reader 300 transmits a non-modulated carrier for producing a reflected wave and performs reception and demodulation of a signal reflected thereto or decoding of image data. The reflected wave reader 300 includes an antenna 301 for the 2.4 GHz band, a circulator 302, a reception section 303, a transmission section 304, a communication control section 305, and a JPEG decoder 306.
As an instruction is provided from the communication control section 305 to the transmission section 304, a non-modulated carrier is transmitted from the reflected wave reader 300. The non-modulated carrier outputted from the transmission section 304 is signaled from the antenna 301 through the circulator 302.
A reflected wave modulated with the image data from the digital camera 200 is received by the reception section 303 through the antenna 301 and the circulator 302 and demodulated by the communication control section 305.
The data demodulated by the communication control section 305 is converted from JPEG data into an analog AV signal (or an NTSC signal) by the JPEG decoder section 306 so that an image of the data can be observed on a television set 307 connected to the reflected wave reader 300. The communication control section 305 performs also communication control with the digital camera 200 and performs transmission of a control signal of delivery confirmation information or the like by ASK through the transmission section 304.
In FIG. 7, reference numeral 308 denotes an infrared reception section. The infrared reception section 308 receives a control signal from the infrared remote controller 108 and issues an instruction to the body of the television set 307.
Here, the inventors of the present invention consider that such a reflected wave transmission system as described has such subjects as described below.
When an image of the digital camera 101 is to be displayed on the television set 106, the user would change over the video input channel first using the infrared remote controller 108. Thereafter, the user would operate the operation/display section 205 of the digital camera 101 to perform selection of an image to be displayed and then perform transmission of image data.
Further, if the user does not perform operations of two devices of the infrared remote controller 108 and the digital camera 101, then the television set 106 cannot display an image, and cumbersome operations are required. Further, it is not considered that various operations on the operation/display section 205 of the digital camera 101 are good in operability also from the size of the operation buttons.
[Patent Document 1]
Japanese Patent Laid-open No. 2004-56711
[Patent Document 2]
Japanese Patent Laid-open No. Hei 01-182782